1. Technical Field
The present invention relates to object position determination using satellites. More specifically, this invention relates to a novel and improved method and system for mobile vehicle position determination, particularly aircraft, using signal propagation time delays through a plurality of communication paths to calculate the vehicle position.
2. Background Art
A need is recognized by many in the mobile vehicle environment for vehicle location information. One industry in particular in which such information is particularly desirable is the commercial trucking industry. Another industry in which such information is also desirable is in the airline industry. In the commercial trucking industry an efficient and accurate method of vehicle position determination is in demand. With ready access to vehicle location information, the trucking company home base obtains several advantages. The trucking company can keep the customer apprised of location, route and estimated time arrival of payloads. The trucking company can also use vehicle location information together with empirical data on the effectiveness of routing, thereby determining the most economically efficient routing paths and procedures.
Heretofore, vehicle location information has been communicated to the trucking company home base by the truck drivers themselves, via telephones, as they reach destinations and stopovers. These location reports are intermittent at best, because they only occur when the truck driver has reached the destination or stopover and can take the time to phone the trucking company home base. These location reports are also quite costly to the trucking company because in effect they cause substantial down time of the freight carrying vehicle. This down time is due to the fact that to make a location report, the tractor driver must remove his vehicle from route, find a telephone which he can use to phone the home base, and take the time to make the location report. This method of location report also leaves room for substantial inaccuracies. For example, truck drivers may report incorrect location information either mistakenly or intentionally; or report inaccurate estimates of times of arrival and departure.
Presently the commerical trucking industry is implementing versatile mobile communication terminals for use in their freight hauling tractors. These terminals are capable of providing two-way communications between the trucking company home base and the truck. Typically the communications are via satellite between the truck and a network communications center or hub. The trucking company is coupled by conventional means, such as telephone lines to the hub.
Using the radio communication capabilities at each mobile terminal to provide vehicle position determination offers great advantages to the commercial trucking industry. Location reports would no longer be intermittent because the trucking company home base could locate a vehicle at will. No down time of the freight hauling vehicle would be required because the communications necessary for determining location could take place while the truck is in route. Also, inaccuracies in location reports would be virtually eliminated because the trucking company home base would be almost instantaneously ascertaining accurate vehicle location information.
Heretofore, methods of object position determination have been relatively inaccurate or required expensive dedicated hardware. One such method is as described in U.S. Pat. No. 4,161,730. This method offers position estimation with occasional accurate position updates. The accuracy of the position estimation is dependent upon the accuracy of a dedicated clock of 10.sup.-10 located at the object whose position is being determined. It also proposes the use of accurate, space qualified, atomic clock standards aboard the satellites such as GOES satellites.
Another well known method of position determination is made by using a conventional LORAN-C system. In this application each mobile unit includes a LORAN-C unit which typically includes an antenna and position sensor/processor. The LORAN-C signals are received at the mobile unit where they are processed. The resulting position determination may then be transmitted to the fixed station.
It is therefore an object of the present invention to provide a novel and improved method for object location as an adjunct to a satellite communication system.
It is another object of the present invention to provide a novel and improved method of object position determination whose accuracy does not require independent and highly precise time keeping equipment located either in the satellites of the system or the object whose position is being determined.
It is a further object of the present invention to introduce a new approach for determining time intervals (hence distance) without maintenance of an absolute time base at the vehicle, contrary to methods as prescribed in U.S. Pat. No. 4,161,730.
It is still further object of the present invention to introduce the use of standard transponder satellite payloads for the purposes of vehicle position determinations. These communication transponders, which are used in the majority of communications satellites, are adequate for relaying the signals used for position determination of the vehicle. Special time and frequency standards within the satellite are not required. It is only necessary to know their characteristics.
It is a further object of the present invention to provide a novel and improved method of vehicle location which does not require vehicle down time.
It is yet another object of the present invention to provide a novel and improved method of vehicle location determination which allows the trucking company or air carrier home base to determine vehicle location at will rather than relying on intermittent reports from a truck driver or pilot.